Project Abstract: Diabetes mellitus (DM) afflicts 26 million people in the US. 40-70% of these diabetics die of cardiovascular complications. We and others found that DM increases reactive oxygen species (ROS)-mediated aldehydes like 4-hydroxy-2-nonenal (4HNE) generation. 4HNE forms covalent bonds with macromolecules known as adducts, which lead to cellular damage and decreased cardiac function. Aldehyde dehydrogenase (ALDH2) is a mitochondrial enzyme that detoxifies 4HNE in the heart. We and others reported that in streptozotocin-induced hyperglycemic models, ALDH2 levels and activity in the heart are reduced, whereas 4HNE protein adducts are increased. Although we think this causes cardiac dysfunction, the exact mechanism is unclear. However, most diabetic patients have type-2 DM. Thus, it is imperative to investigate whether hyperglycemia-induced 4HNE and lower ALDH2 activity contribute to cardiac dysfunction in type-2 DM models. We recently demonstrated that high glucose stress or 4HNE administration decreased mitochondrial respiration with increased mitochondrial DNA (mtDNA) damage in cultured cardiomyocytes. In our preliminary study using type-2 diabetic mouse heart, we found an increase in mitochondrial levels of 8-hydroxyguanine (8OHG), an oxidized mtDNA product. 8- oxoguanine glycosylase (OGG)-1 is responsible for identification and excision of 8OHG. Next, we found increased 4HNE adduct formation on OGG-1 and reduced OGG-1 levels. These data suggest that 4HNE adduction on OGG-1 reduces its level and activity thereby raising the unmetabolized 8OHG level. Thus we postulate that 4HNE-mediated mtDNA damage is part of the mechanism by which lower ALDH2 activity causes mitochondrial respiratory dysfunction. To test our idea, we will use a high-fat diet induced type-2 DM model in wild type (WT) C57BL/6 and ALDH2*2 mutant mice. This mutation mimics East Asians with the E487K variant (ALDH2*2), which exhibits lower ALDH2 activity. We will treat our diabetic mice with Alda-1, the only specific drug available to improve the catalytic activity of both WT and mutant ALDH2. We propose following three specific aims: Aim 1- Hyperglycemia in models of type-2 diabetes reduces ALDH2 activity in the heart by increasing 4HNE adduction with ALDH2, further leading to cardiac dysfunction: Aim 2- Reduced ALDH2 activity leads to increased 4HNE adduct formation on mtDNA and 8-oxoguanine glycosylase (OGG)-1, a mtDNA repair enzyme, thereby causing mtDNA damage and poor mitochondrial respiration in type-2 DM: AIM 3-Augmenting ALDH2 activity ameliorates cardiac function in type2-DM. This study will identify a novel role of ALDH2 in hyperglycemia mediated cardiac dysfunction and establish that ALDH2 could be a therapeutic target for restoring cardiac function in DM patients.